Knife sharpener



FIG. 1 is a front perspective view of a knife sharpener showing our newdesign;

FIG. 2 is a left side elevational view thereof;

FIG. 3 is a right side elevational view thereof;

FIG. 4 is a top plan view thereof;

FIG. 5 is a bottom plan view thereof;

FIG. 6 is a front elevational view thereof;

FIG. 7 is a rear elevational view thereof.

The ornamental design for a knife sharpener, as shown and described.